A technology described in Technological Disclosure No. 2004-504490 of the Japan Institute of Invention and Innovation for example has been proposed as a vehicle-body underside airflow controller.
The technology described in Technological Disclosure No. 2004-504490 of the Japan Institute of Invention and Innovation proposes to obtain optimum aerodynamic characteristics by providing a rear diffuser (or may be a floor pan or an under-cover) at the rear of the vehicle over a rear wheel at the underside of the body and by controlling a road clearance (a height from a road surface) of the rear diffuser.
Specifically, it improves straight-driving stability and steering stability of the vehicle by controlling the road clearance of the whole rear diffuser and by controlling the road clearance of the rear diffuser in the lateral direction part of the vehicle according to vehicle speed, a yaw rate and acceleration in the lateral direction of the vehicle (so-called lateral G).
However, the technology described in Technological Disclosure No. 2004-504490 of the Japan Institute of Invention and Innovation only adjusts the height of the rear diffuser from the road surface and does not change a rise angle of the rear diffuser (an angle between an extension line of the rear diffuser and the road surface) that has been set at an angle in advance.
The rise angle of the rear diffuser affects the aerodynamic performance of the vehicle and is deeply connected with contradictory requirements such as interference with the road surface and looks, so that it has been desired to be able to obtain the optimum aerodynamic characteristics.